The lamps were destroyed by an assault by Melkor. Their fall was cataclysmic: The symmetry of Arda was destroyed as the weight of the lamps broke continents and their fire burned the land, such that the original design of the Valar was undone forever, including Almaren. The Valar did what they could to hinder the damage and their Enemy and his hosts fled back to Utumno. As they didn't know the time and place of the Children of Eru, they were afraid to rend the Earth again.[1]

At the site where Illuin fell, the inland Sea of Helcar was formed, of which Cuiviénen was a bay. There was also the Sea of Ringil to the south, perhaps associated with the roots of Ormal.

Almaren was also destroyed, and after repairing some of the damage done by the resulting tumult, the Valar left Middle-earth for Valinor. There the Valar created the Two Trees, which were also a pair of gold and silver light, as the Two Lamps before them.

According to older writings not used in the published The Silmarillion, the Valar wanted peace with Melkor, and decided to ask his assistance: they wished to fix the lamps upon Arda's ground. Melkor, black with hate and envy of the rest of the Valar, agreed to help. He gave Aulë a substance which was both sturdy and strong: ice, which was unknown to the Valar. Melkor bided his time and allowed the Valar to do as they wished until the fateful day when the Lamps' light and heat melted the ice and crashed upon Arda, flooding it with water and darkness.

The one remaining influence from the older version of the story was that the fall of the towers created inland seas, a vestige of the notion that the towers had been made of ice that melted.[2]

In Tolkien's latest writings where Arda was a round world from its beginning, the Two Lamps never truly existed and were instead a subject of Númenórean mythology.[3]